Magnetic focus rings for improved copper plating

ABSTRACT

A method and system wherein magnets are employed on the outside of a plating bath chamber to control the field lines that are used during the plating process. By being able to control the field lines during the plating process, improved gap fill and uniformity can be achieved. The magnetic field acting on the bath can be continuous, pulsed, stressed (i.e., the shape of the field can be changed), sinusoidal, etc. The magnetic field can be modulated as function of time to produce a desired copper uniformity on the wafer. It is anticipated that there is no limit to how the shape of the magnets or magnetic field can be configured and controlled to achieve the desired result for both fill of deep contacts and the uniformity needed to match the succeeding polishing process.

BACKGROUND

The present invention generally relates to methods and systems fordepositing metal on a substrate, such as depositing copper on asemiconductor wafer. The present invention more specifically relates tothe use of a magnetic filed, such as with magnetic focus rings, toimprove copper plating.

In the semiconductor industry, copper wire interconnects are becomingthe process of record for 0.13 micron processing node and smaller. Thecurrent technology used for this process is electro-chemical-deposition(ECD). Many companies manufacture tools for this process. The finalcopper uniformity of the deposition needs to match the uniformity of theCMP process as much as possible from center to edge before the wafergoes into the post polishing process (either chemical mechanicalpolishing (CMP) or electro-polishing). If the non-uniformity of thefinal film and polishing processes are not matched, there are problemswith the devices. Another problem is gap fill. As dimensions getsmaller, technology is relying more on the chemistry to assist gap fill.However, voids are still a major problem with regard to the newtechnologies which are being used.

Typically, current tool designs are very similar to each other, exceptfor differences in the design of the plating cell head which holds thewafer (and which operates as the cathode in the plating process), thecell body (which is the bath tank for the plating solution), and theanode (which is the source of the copper ions which become deposited onthe wafer). In the industry, tool suppliers provide a plumbing,re-circulation, and filtration system for supplying the electrolytesolution to the surface of the wafer in the presence of an electricfield. As shown in FIG. 1, a DC source 10 is used to apply a field froma copper anode 12 to a wafer (the cathode) 14 in a plating bath chamber16, and Cu2+ copper ions follow field lines 18 to the surface 20 of thewafer 14. In attempts to control the uniformity, each of the vendorsthat manufacture a tool for this process has designed a different cellhead, a different bath structure, and different anode configurations.However, all of these designs still yield a level of non-uniformity thatmust be dealt with in future processing steps. Other attempts usingdifferent chemical formulations have also been devised to deal with theproblems of non-uniformity of deposit and the presence of voids.

Generally, existing solutions have not solved the uniformity and gapfill problems associated with deposition of copper on a semiconductorwafer. In fact, some of the designs have introduced additional problemsthat are difficult to eliminate, such as edge particles caused by thecontact ring, or bulk defects caused by the chemistry.

OBJECTS AND SUMMARY

An object of an embodiment of the present invention is to provide amethod and system which can be used to deposit copper uniformly onto awafer.

Another object of an embodiment of the present invention is to provide amethod and system which deposits copper onto a wafer such that there isno gap fill problem.

Briefly, and in accordance with at least one of the foregoing objects,an embodiment of the present invention provides a method and systemwherein magnets are employed proximate, such as on the outside of, aplating bath chamber to control the field lines that are used during theplating process. By being able to control the field lines during theplating process, improved gap fill and uniformity can be achieved.

The magnetic field acting on the bath can be continuous, pulsed,stressed (i.e., the shape of the field can be changed), sinusoidal, etc.The magnetic field can be modulated as function of time to produce adesired copper uniformity on the wafer. It is anticipated that there isno limit to how the shape of the magnets or magnetic field can beconfigured and controlled to achieve the desired result for both fill ofdeep contacts and the uniformity needed to match the subsequent polishprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

The organization and manner of the structure and operation of theinvention, together with further objects and advantages thereof, maybest be understood by reference to the following description, taken inconnection with the accompanying drawing, wherein:

FIG. 1 illustrates a prior art system for depositing copper on thesurface of a semiconductor wafer;

FIG. 2 illustrates a system for depositing copper on the surface of asemiconductor wafer, wherein the system is in accordance with anembodiment of the present invention;

FIG. 3 provides a top view, showing magnets positioned around thecircumference of the bath chamber;

FIG. 4 provides a flow chart of a method which can be used in connectionwith the system shown in FIG. 2, wherein the method is in accordancewith an embodiment of the present invention.

DESCRIPTION

While the invention may be susceptible to embodiment in different forms,there are shown in the drawings, and herein will be described in detail,specific embodiments of the invention. The present disclosure is to beconsidered an example of the principles of the invention, and is notintended to limit the invention to that which is illustrated anddescribed herein.

FIG. 2 illustrates a system 30 for depositing copper on the surface 20of a semiconductor wafer 14, wherein the system 30 is in accordance withan embodiment of the present invention. The system 30 provides thatmagnets 32 are positioned proximate a bath housing 16. While the magnets32 may possibly be placed within the bath housing 16 if properlyinsulated, as shown in FIG. 3 preferably the magnets 32 are positionedon the outside of the bath housing 16, around its circumference or outerperimeter 34. Regardless, the magnets 32 are used to provide a magneticfield to improve uniformity and gap fill. Specifically, a DC source 10is used to apply a field from a copper anode 12 to a wafer (the cathode)14 in a plating bath chamber 16, and Cu2+ copper ions follow field lines40 to the surface 20 of the wafer 14. The magnets 32 are used toeffectively modify the field lines 40 so that they are more linearbetween the anode (i.e., the copper) 12 and the cathode (i.e., thewafer) 14 (i.e., compare the field lines 18 illustrated in FIG. 1 to thefield lines 40 illustrated in FIG. 2).

The magnets 32 may be permanent magnets and/or controllableelectro-magnets. If at least some of the magnets 32 are electro-magnets,a control system 42 is connected to the electro-magnets and is operableto modulate the magnets to provide a desired magnetic filed such thatthe filed lines 40 between the anode 12 and cathode 14 are tuned asdesired to improve both uniformity of copper deposit and improve gapfill. The magnetic field acting on the bath can be continuous, pulsed,stressed (i.e. the shape of the field can be changed), sinusoidal, etc.There is no limit to how the shape of the magnets or magnetic field canbe configured and controlled to achieve the desired result for both fillof deep contacts and the uniformity needed to match the polish process.

The typical uniformity problems seen on plated wafers manifests itselfas a bulls eye, center to edge pattern. By modulating the intensity ofthe magnetic field, the shape and intensity of the field lines producedby the power supply connected to the cathode and anode can be altered toproduce a desired uniformity pattern on the wafer. The shapes of themagnetic field can also be controlled such that the intensity can bemodulated at any area of the bath. The magnetic fields generated wouldforce the field lines to be vertical in both the center of the wafer andat the edge of the bath allowing the migrating copper ions to arrive atthe surface of the wafer “more vertical” therefore more successfully infilling the deep gaps in both the center of the wafer and the edge ofthe wafer.

Preferably, the control system 42 is configured such that the magneticfiled is modulated over time. Improved vertical plating at the edge ofthe wafer is more important at the beginning of the plating process. Asthe contacts fill, the high aspect ratio decreases. As this happens,preferably the magnetic filed is modulated so that the field lines arechanged to go from “the best fill” to the most desired uniformity tomeet the needs of the polish process.

The present invention provides that fixed or electrically controlledmagnets are used in association with a plating bath chamber to controlthe field lines that are used during the plating process. By controllingthe field lines during the plating process, improved gap fill anduniformity can be achieved. None of the currently availableelectroplating tools on the market utilize such a method of field linecontrol for uniformity or gap fill improvement.

FIG. 4 shows a flow chart of at least one embodiment of this invention.Box 100 explains the basic electroplating process and box 102 explainsthe improved copper deposition process by the utilization of acontrolled magnetic field to improve deposition uniformity.

While embodiments of the present invention are shown and described, itis envisioned that those skilled in the art may devise variousmodifications of the present invention without departing from the spiritand scope of the appended claims.

1. A method for using an anode to plate a cathode with ions in a bathchamber, comprising: applying a voltage to the anode and the cathode,the anode and cathode being disposed in the bath chamber, therebycausing ions to flow along field lines from the anode to the cathode inthe bath chamber and plate the cathode; and using at least one magnet toadjust the field lines.
 2. A method as recited in claim 1, wherein theanode comprises copper and the cathode comprises a wafer.
 3. A method asrecited in claim 1, wherein the step of using at least one magnet toadjust the field lines comprises using a plurality of permanent magnets.4. A method as recited in claim 1, wherein the step of using at leastone magnet to adjust the field lines comprises using a plurality ofelectro-magnets.
 5. A method as recited in claim 1, wherein the step ofusing at least one magnet to adjust the field lines comprises using acontrol system and a plurality of electro-magnets connected to thecontrol system.
 6. A method as recited in claim 1, wherein the step ofusing at least one magnet to adjust the field lines comprises using aplurality of magnets which are disposed outside of the bath chamber. 7.A method as recited in claim 1, wherein the step of using at least onemagnet to adjust the field lines comprises using a plurality of magnetswhich are disposed outside of the bath chamber, around a circumferenceof the bath chamber.
 8. A method as recited in claim 1, wherein the stepof using at least one magnet to adjust the field lines comprises using aplurality of magnets and controlling the magnets such that the magnetsprovide a magnetic field which is at least one of continuous, pulsed,stressed and sinusoidal.
 9. A method as recited in claim 1, wherein thestep of using at least one magnet to adjust the field lines comprisesusing a plurality of magnets and controlling the magnets such that themagnets provide a magnetic field which is modulated over time.
 10. Aplating system comprising: a bath chamber; an anode disposed in the bathchamber; a cathode disposed in the bath chamber; a voltage sourceconnected to the anode and cathode, wherein application of voltagecauses ions to flow along field lines from the anode to the cathode inthe bath chamber and plate the cathode; and at least one magnet disposedproximate the bath chamber, wherein said at least one magnet adjusts thefield lines.
 11. A system as recited in claim 10, wherein the anodecomprises copper and the cathode comprises a wafer.
 12. A system asrecited in claim 10, wherein said at least one magnet comprises aplurality of permanent magnets.
 13. A system as recited in claim 10,wherein said at least one magnet comprises a plurality ofelectro-magnets.
 14. A system as recited in claim 13, further comprisinga control system connected to the plurality of electro-magnets.
 15. Asystem as recited in claim 10, wherein said at least one magnetcomprises a plurality of magnets which are disposed outside of the bathchamber.
 16. A system as recited in claim 10, wherein said at least onemagnet comprises a plurality of magnets which are disposed outside ofthe bath chamber, around a circumference of the bath chamber.
 17. Asystem as recited in claim 14, wherein the control system is configuredto control the electro-magnets such that the electro-magnets provide amagnetic field which is at least one of continuous, pulsed, stressed andsinusoidal.
 18. A system as recited in claim 14, wherein the controlsystem is configured to control the electro-magnets such that theelectro-magnets provide a magnetic field which is modulated over time.